(a) Fields of the Invention
The present invention relates to a semiconductor device fabrication method and particularly relates to a copper interconnect formation step included in a fabrication process of a semiconductor device.
(b) Description of Related Art
In recent years, semiconductor products made of silicon have become finer and more sophisticated. Accompanied with this trend, the semiconductor products make heavy use of copper interconnects. However, it is extremely difficult to subject copper to dry etching. Therefore, the following method for forming a copper interconnect (damascene technique) is typically employed which includes a series of steps of: forming an interconnect groove by dry etching of an insulating film; forming a barrier film in the formed interconnect groove by sputtering technique and then filling the groove with copper by electrolysis plating; and removing excess-barrier and copper films present outside the interconnect groove and planarizing the surface by chemical mechanical polishing.
In the above-described step of performing chemical mechanical polishing in the damascene technique, after the copper and barrier films are subjected to chemical mechanical polishing, a cleaning process is performed for removing particles such as abrasive and metal contaminants remaining on a substrate surface, and then a drying process is performed on the substrate. A currently dominant system for such a procedure is a so-called dry-in, dry-out system in which a series of processes of chemical mechanical polishing, cleaning, and drying is carried out within the same apparatus, and apparatuses operating in this system go mainstream. An exemplary chemical mechanical polishing apparatus capable of carrying out this through process is proposed in Japanese Unexamined Patent Publication No. 2000-36477. The proposed apparatus carrying out a through process of polishing, cleaning, and drying is characterized in that in order to keep the cleanliness of a cleaning and drying unit, a water flow separates an atmosphere in a polishing unit from an atmosphere in the cleaning and drying unit. Also, for example, Japanese Unexamined Patent Publication No. 2003-51481 proposes an apparatus characterized in that in order to enhance the throughput of a chemical mechanical polishing apparatus, two or more drying rooms are provided in the subsequent stage of a cleaning process unit to allow a parallel drying process. These conventional apparatuses carrying out a through process employ, as a drying mechanism, spin drying technique, dry gas blowing technique, lamp heating technique, or IPA drying technique.
Recently, a problem has arisen that moisture still remaining on the substrate after the polishing and clearing processes described above affects the reliability of a copper interconnect. Specifically, in the case where there is moisture on the surface of a portion of an insulating film provided between copper interconnects after chemical mechanical polishing, if the substrate in this state is let to stand for more than a given period of time until the next process is conducted thereon, part of copper constituting the interconnect migrates (moves) due to that moisture. This results in creation of a thin copper layer on the insulating film. The thin copper layer thus created grows by a current flowing through the interconnects during operation of the semiconductor device. If the growing copper finally reaches the adjacent interconnect, a short circuit may be made between the interconnects.
FIGS. 7A to 7D are plan views for illustrating the mechanism of occurrence of failure causing the short circuit between the interconnects mentioned above. Note that FIGS. 7A to 7D show copper interconnects 101 provided with barrier films formed in interlayer insulating films 100, and also show the state in which moisture remains in a portion of the interlayer insulating film 100 positioned between the copper interconnects 101.
As shown in FIGS. 7A to 7D, the moisture 102 remaining in the portion of the interlayer insulating film 100 positioned between the copper interconnects 101 causes migration 103 of copper constituting the interconnects 101 (see FIG. 7B). When this migration is developed (see FIG. 7C), a short circuit failure 104 between the interconnects will finally arise (see FIG. 7D). Such an occurrence of short circuit failure between the interconnects may in turn cause defects of the fabricated semiconductor product, so that this is a big problem for the reliability of the semiconductor product. Therefore, it is important to sufficiently remove the moisture remaining on the substrate after chemical mechanical polishing.
After the chemical mechanical polishing is performed in the damascene technique mentioned above, as shown in a plan view of FIG. 8A and a sectional view of FIG. 8B, defects 202 caused by copper corrosion are likely to be created on the surface of the copper interconnect 201 provided with the barrier films formed in the interlayer insulating film 200 on the substrate. Thus, since the copper corrosion defects 202 are likely to be created on the surface of the copper interconnect 201 formed in the interlayer insulating film 200, a treatment for preventing the surface of the copper interconnect 201 from corroding is required by the time a film formation step is implemented as the next process step. Generally, the treatment for preventing this corrosion is performed in such a manner that an anticorrosive is added to an abrasive used for chemical mechanical polishing of the barrier film to subject the surfaces of the copper interconnects to anticorrosive treatment during the chemical mechanical polishing of the barrier film. As the anticorrosive, use is made of triazole-based compounds, their derivatives, or water-soluble agent containing their mixture. Among them, the most commonly used anticorrosive is benzotriazole (BTA). BTA reacts with copper to produce a stable compound, Cu—BTA, and the produced Cu—BTA is used as a coating to prevent corrosion of the copper interconnect. In addition, Japanese Unexamined Patent Publication No.2001-196379 proposes a method which includes the step of applying, to a substrate, a solution with not an abrasive but an anticorrosive contained therein to form an anticorrosive layer after or during chemical mechanical polishing.